Originally to be directed by Walter Hill, but he pulled out and gave the job to Ridley Scott.

Veronica Cartwright was originally to play Ripley, but producers opted for Sigourney Weaver.

An early draft of the script had a male Ripley.

Conceptual artist H.R. Giger's designs were changed several times because of their blatant sexuality.

Roger Dicken, who designed and operated the "face hugger" and the "chest burster," had originally wanted the latter to pull itself out of Kane's torso with its own little hands, a sequence he felt would have produced a much more horrifying effect than the gratuitous blood and guts in the release print.

Much of the dialogue was ad-libbed.

In the scene where Dallas, Kane and Lambert are leaving the ship, the actual actors walking past the Nostromo's landing struts are three children (two of whom were Ridley Scott's children dressed in scaled down spacesuits). This has the effect of making the ship look bigger. H.R. Giger complained about the scene because he had not finished painting the space jockey.

The front (face) part of the alien costume's head is made from a cast of a real human skull.

Ridley Scott is reportedly quoted as saying that originally he wanted a much darker ending. He planned on having the alien bite off Ripley's head in the escape shuttle, sit in her chair, and then start speaking with her voice in a message to Earth. Apparently, 20th Century Fox wasn't too pleased with such a dark ending.

During production an attempt was made to make the alien character transparent or at least translucent.

Three aliens were made: a model and two suits. One of the suits was for the seven foot tall Masai tribesman Bolajo Bolaji, and the other was for a trained stunt man.

The models had to be repainted every evening of the shoot because the slime used on-set removed the acrylic paint from their surfaces.

The rumor that the cast, except for John Hurt, did not know what would happen during the "chestburster" scene is partly true. The scene had been explained for them, but they did not know specifics. For example, Veronica Cartwright did not expect to be sprayed with blood.

The thin layer of mist that "notified the eggs" was made possible using a pulsating laser and smoke, borrowed from the band The Who.

"Nostromo" is the title of a Joseph Conrad book. The shuttle that Ripley escapes on is called the "Narcissus", a reference to another Conrad book. See also Aliens (1986).

The vector graphics that appear on Ripley's screen showing the undocking sequence for the Nostromo were also used for the aircar launch sequence in Blade Runner (1982)).

Extra scenes filmed but not included, due to pacing problems:

Ripley finds Dallas and Brett cocooned. Dallas is covered in maggots and begs Ripley to kill him. She does so with a flamethrower.

Ripley and Lambert discuss whether Ash has sex or not.

Alternative death scene for Brett: Ripley and Parker come across an alive Brett being lifted from the ground.

Many of the non-English versions of the film's title translate as something similar to "Alien: The 8th Passenger".

The alien's habit of laying eggs in the stomach (which then burst out) was inspired by the spider wasp (ichneumonid) that lays its eggs in the abdomen of spiders. This image gave Dan Obannon nightmares, which he used in creating the story.

A lawsuit by A.E. van Vogt, claiming plagiarism of his 1939 story "Discord in Scarlet" (which he had also incorporated in the 1950 novel "Voyage of the Space Beagle"), was settled out of court.

A sex scene between Dallas and Ripley was in the script, but was not filmed.

The laserdisc release features a separate section with the scenes not included in the theatrical release. This is the new material:

After being awakened from hypersleep, Kane wanders out to the kitchen to prepare breakfast; he says "Rise and shine Lambert".

The crew gathers on the bridge and listens to the signal coming from the derelict craft.

Lambert confronts Ripley about Ripley's reluctance to let them back on the ship with Kane and the facehugger. Lambert tells Ripley, Parker and Brett how the face hugger got on Kane.

Ripley radios down to Parker and Brett to see how they're progressing on the repairs, Parker and Ripley exchange tense words over the radio.

After the face hugger's acid eats through a few floors, the crew returns to the med lab to check up on Kane's condition. Ripley sees an X-Ray of Kane's chest and asks Ash, "What is that dark stain on Kane's lung?" The rest of the crew starts asking if Kane's going to live, Dallas tells everyone to go back to work.

After Kane's death, the crew gathers around at the meal table to discuss what they're going to do with the escaped alien. Brett announces the cattle-prod idea and suggests "catching" the alien in a net.

Longer version of Brett's death. This scene had Brett frozen with fear as the alien grabs his head; he yells "Parker!" and then blood pours from beneath his cap. The alien lifts him up into the landing gear and Ripley and Parker come rushing in. Parker stands where Brett once was and looks up. Blood drips on his shirt and then Brett's cattle prod falls to Parker's feet.

Part of a scene that involves Parker, Ripley and Lambert trying to flush the alien out of the air lock. As they are about to succeed, an alarm is triggered and the alien rushes out of the airlock (getting its tail caught in the closing door, and spilling acid that causes a hull breach). Parker falls unconsciously to the floor, Ripley does the same and Lambert and Ash come to their rescue. Ripley vocalizes her suspicions about Ash by accusing him of setting the alarm off.

The build-up to Lambert's death is much longer. (Watch the alien's shadow on the wall, it walks in, crouches down, then immediately gets up) A scene where we see the alien enter, crouch down and wait until Lambert notices its presence was cut. When Lambert sees the alien, it uncoils its tail and walks (like a crab) over to Lambert.

After Ripley discovers the remains of Parker and Lambert, she makes another discovery. Ripley enters the landing gear area of the Nostromo (where Brett got killed) and discovers a cocooned Dallas and Brett mutating into an egg. Dallas pleads, "Kill me". Ripley flames Dallas and the Brett-egg and then runs to set the ship on self-destruct.

The latest video release of Alien in Norway has been severely cut. There are no indications given on the cassette box that this has been done. Total playing time missing is about 15 minutes. Key noticeable scene cuts include Kane's apparent revival, and subsequent chest bursting scene; Ash's demise.

The picture and the Dolby Digital soundtrack used to make the THX laserdisc were mastered from the 70 mm release version. The soundtrack contains therefore some alternate dialogue, rough sound editing, different/enhanced sound effects, and is missing some dialogue that was contained on the Dolby Stereo sound mix of the 35 mm version.